While carbon dioxide increases are estimated to be the single biggest contributor to the human-induced forcing of climate change, other species have also perturbed the climate system. This session will focus on the physical and chemical aspects of these non–carbon dioxide species; how they have forced the climate system; how they will contribute in the future; what are the telltale signatures of these agents; what have been and will be the impacts of these changes on climate, including precipitation and air quality; how to improve the level of confidence in the scientific knowledge; and how can the knowledge be framed as inputs into decision-making. Important advancements have occurred in the scientific understanding of the processes governing the climate- and air quality–relevant properties using observations and models. Of particular interest are the effects of the non–carbon-based greenhouse gases, including stratospheric and tropospheric ozone, and the different types of aerosols on the key climate variables such as temperature and rainfall. The geographical distribution and temporal variations of the climate change due to these species are to be compared with those estimated for carbon dioxide–related changes, with the impacts becoming significant considerations for adaptation and mitigation decisions. The scientific basis, including the characterization and quantification of uncertainties, enables sound inputs into the policy discussions.